In a wireless telecommunication system, radio channels provide a physical link between communication units. The wireless communication units in such a system typically include a base station processor in communication with a network such as the Public Switchboard Telephone Network (PSTN), in the case of voice communication, or a data network, in the case of data communication, and one or more subscriber access units in communication with a plurality of end user computing devices, such as user PCs. The wireless channels include forward channels, for message transmission from the base station processor to the subscriber access units, and reverse channels, for message transmission to the base station processor from the subscriber access units.
In the case of a wireless data system such as may be used to provide wireless Internet access, each base station processor typically serves many subscriber access units, which in turn serve many end user computing devices. The wireless channels, however, are a scarce resource, and are therefore allocated by a scheduler among the subscriber access units served by the base station processor. The scheduler allocates the wireless channels among the subscriber access units on a traffic demand basis. One way of supporting on demand access among multiple users is so-called time division multiple access (TDMA) whereas each of the wireless channels are allocated to specific connections only for a certain predetermined time intervals or time slot. Message transmission is initiated at the beginning of each time slot. A message queued for transmission via a wireless channel, therefore, remains queued until the beginning of the next time slot. The rate and duration of the time slots, therefore, define a message transmission cycle.
Often, a message transmission results in a return message being transmitted back to the sending wireless communication unit. Frequently, the return message is computed and queued for transmission in less than the predetermined interval defining the time slots. The return message may even be computed and enqueued in less than one half the duration of a time slot. However, the return message must still wait enqueued until the next allocated time slot becomes available to the particular connection. Therefore, transmission of the message and the return message requires at least three time slots: one to transmit the message, a second during which the return message is computed, and a third to transmit the return message, even if the return message was computed well before the second time slot completed.
Further, some channel allocation methods allocate a wireless channel for the return message at the same time as allocating a channel for the initial message which triggered the return message. The wireless channel allocated for the return message, therefore, remains allocated until the return message is received.
It would be beneficial, therefore, to provide a system and method for scheduling the time slots such that the forward cycle and the reverse cycle are out of phase, therefore providing a time slot for a return message in less than a full time slot interval.